1. Field of the Invention
This invention relates to an improved wheel supporting bearing unit which is used to rotatably support a wheel and a brake rotary member relative to a suspension system and a manufacturing method for the same.
2. Description of the Background Art
A wheel supporting bearing unit has conventionally been in use to rotatably support an automotive wheel relative to a suspension system. FIG. 17 shows, as a first example of a conventionally known wheel supporting bearing unit like this, a wheel supporting bearing unit for driving wheels (front wheels of an FF vehicle, rear wheels of FR and RR vehicles, and all wheels of a 4WD vehicle). This wheel supporting bearing unit includes an outer ring 1, a hub 2 and a plurality of tapered rollers 3, 3 each constituting a rolling element. Among these, the outer ring 1 has a primary and secondary outer ring raceways 4a, 4b which are each formed on an inner circumferential surface into a coned recessed surface and a connecting flange 5 which is formed on an outer circumferential surface thereof. The inclined directions of the primary and secondary outer ring raceways 4a, 4b are opposite to each other.
In addition, the hub 2 is made up of a combination of a hub main body 6 and a primary and secondary inner rings 7a, 7b. Of these, the hub main body 6 has a mounting flange 8 which is formed at a portion on an outer circumferential surface thereof which is close to an outboard end (in this application, axially outboard means outboard in a width direction of a vehicle in such a state that the bearing unit is mounted on the vehicle. The left-hand side in FIGS. 6, 17 to 28 and the upper side in FIGS. 7, 9 correspond to the axially outboard. In contrast, the right-hand side in FIGS. 6, 17 to 28 and the lower side in FIGS. 7, 9 denote axially inboard) for fixedly supporting a wheel and a brake rotor which is a brake rotary member, a cylindrical surface portion 9 which is formed from a central portion to an inboard end portion on the outer circumferential surface thereof and a splined hole 10 which is formed in a central portion thereof. In addition, at a plurality of locations in a circumferential direction of the mounting flange 8 (for example, five locations which are positioned circumferentially at equal intervals), circular holes 11, 11, which are supporting holes, are formed in such a manner as to axially pass through the flange at portions which are equidistant from a center axis of the mounting flange 8 (the hub 6). Then, studs 12, 12, which are rod-shaped members, are fitted and supported in these circular holes 11, 11 through press fit. These studs 12, 12 are used to fixedly support the wheel and the brake rotor on the mounting flange 8.
In addition, the primary inner ring 7a has a primary inner ring raceway 13a which is formed into a coned raised surface on an outer circumferential surface thereof, and the secondary ring 7b has a secondary inner ring raceway 13b which is formed into a coned raised surface on an outer circumferential surface thereof. Additionally, these primary and secondary inner rings 7a, 7b have small collar portions 14 and large collar portions 15 which are formed at small diameter side end portions and large diameter side end portions, respectively, of the primary and secondary inner ring raceways 13a, 13b in such a manner as to protrude radially outwards, as well as extend along the full circumference of the primary and secondary inner rings, respectively. In addition, inner circumferential surfaces of the primary and secondary inner rings 7a, 7b are each formed into a simple cylindrical surface. These primary and secondary inner rings 7a, 7b, which are configured described above, are fitted and supported on the cylindrical surface portion 9 of the hub main body 6 through interference fit in such a manner that small diameter side end faces thereof are brought into abutment with each other. Additionally, in this state, a large diameter side end face of the primary inner ring 7a is abutted against an stepped surface 16 provided at a proximal end portion of the cylindrical surface portion 9, and a large diameter side end face of the secondary inner ring 7b protrudes axially further inwards than an inner end face of the hub main body 6. The plurality of tapered rollers 3, 3 are rollingly provided between the primary and secondary outer ring raceways 4a, 4b and the primary and secondary inner ring raceways 13a, 13b, respectively.
When assembling the wheel supporting bearing unit on to a motor vehicle, as shown in the figure, a splined shaft 18, which is a drive axle fixedly provided at a central portion of an outboard end face of a constant velocity joint outer ring 17, is inserted into the splined hole 10. An outside diameter side portion of the outboard end face of the constant joint outer wheel 17 is abutted against the large diameter side end face of the secondary inner ring 7b. Then, in this state, a nut 20 is screwed on an externally threaded portion 19 provided at a distal end portion of the splined shaft 18 which protrudes from the splined hole 10, and tightened further thereon. Due to this configuration, the splined shaft 18 and the hub 2 are coupled and fixed to each other, and by imparting forces to the primary and secondary inner rings 7a, 7b which acts to make them approach each other with respect to the axial direction, a proper preload is imparted to the individual tapered rollers 3, 3. Note that, large diameter side end faces (or end edges) of the individual tapered rollers 3, 3 are guided to respective inner faces 21, 21 of the large collar portions 15, 15 which constitute collar faces, respectively. The connecting flange 5 is coupled and fixed to a knuckle 22 which makes up the suspension system using a bolt 23. A wheel and a brake rotor, neither of which is shown, are fixedly supported on the mounting flange 8 using the individual studs 12, 12. In a case where the illustrated construction, an axially outboard surface of the mounting flange 8 constitutes a mounting surface 24 of the brake rotor.
Next, FIG. 18 shows a second example of a conventionally known wheel supporting bearing unit. In the case of this second example of the wheel supporting bearing unit, a clamping portion 25 is formed by plastically deforming in a radially outward direction a cylindrical portion which protrudes axially further inboards than a large diameter side end face of a secondary inner ring 7b at an inboard end portion of a hub main body 6a. In addition, the large diameter side end face of the secondary inner ring 7b is pressed towards an stepped surface 16 provided on an outer circumferential surface of an intermediate portion of the hub main body 6a by the clamping portion 25 so formed. The configurations and functions of the other portions of this example are the same as those of the first embodiment.
Next, FIG. 19 shows a wheel supporting bearing unit for non-driving or driven wheels (rear wheels of an FF vehicle and front wheels of FR and RR vehicles) as a third example of a conventionally known wheel supporting bearing unit. Since this wheel supporting bearing unit of the third example is such as for driven wheels, a splined hole is not provided in a central portion of a hub main body 6b. Instead, an externally threaded portion 26 is provided at an inboard end portion of the hub main body 6b. Then, a large diameter side end face of an inner ring 7b is pressed towards an stepped surface 16 formed on an outer circumferential surface of an intermediate portion of the hub main body 6b by a nut 27 which is screwed on the externally threaded portion 26 and is then tightened further. The configurations and functions of the other portions are the same as those of the first example. Note that although not shown in the drawings, also in the event of the wheel supporting bearing unit for driven wheels, as with the second example that has been described before, there may exists a case where a clamping portion is formed at an inboard end portion of the hub main body so as to press a large diameter side end face of a secondary inner ring by the clamping portion so formed.
Next, FIGS. 20 to 22 show fourth to sixth examples of conventionally known wheel supporting bearing units, respectively. In the case of the first to third examples shown in FIGS. 17 to 19, the primary inner ring raceway 13a is formed on the outer circumferential surface of the primary inner ring 7a fitted on the intermediate portion of the hub main body 6, 6a, 6b. In contrast to this, in the case of the fourth to sixth examples shown in FIGS. 20 to 22, respectively, a primary inner ring raceway 13b is formed direct on an outer circumferential surface of a hub main body 6c to 6e. The configurations and functions of the other portions are the same as those of the aforesaid first to third examples.
Next, FIGS. 23 to 28 show seventh to twelfth examples of conventionally known wheel supporting bearing units, respectively. In the case of the first to sixth examples shown in FIGS. 17 to 22, the tapered rollers 3, 3 are used as a plurality of rolling elements. In contrast to this, in the case of the seventh to twelfth examples shown in FIGS. 23 to 28, balls 28, 28 are used as a plurality of rolling elements. In association with this, bus bars of primary and secondary outer ring raceways 4c, 4d and primary and secondary inner ring raceways 13c, 13d are formed into an arc-like shape. The other configurations and functions of the examples are the same as those of the first to sixth examples. Note that in general, the wheel supporting bearing units utilizing the tapered rollers 3, 3 as the plurality of rolling elements are used as wheel supporting bearing units for motor vehicles of relatively heavy weights, whereas the wheel supporting bearing units utilizing balls 28, 28 are used as wheel supporting bearing units for motor vehicles of relatively light weights.
Incidentally, in the event that the rotational run-out (an axial run-out (displacement amount) in association with rotation) of the brake rotor increases while the vehicle is driven, abnormal noise referred to as judder is generated when the brakes are applied. In order to prevent the occurrence of the judder due to such a cause, the rotational run-out of the brake rotor needs to be suppressed. In order to suppress the rotational run-out of the brake rotor, perpendicularity of the mounting surface 24 of the brake rotor relative to the rotational center axis of the hub 2, 2a to 2k and plane accuracy of the mounting surface 24 needs to be improved, respectively.
Of these, the plane accuracy of the mounting surface 24 is deteriorated by elastic deformation or plastic deformation of the mounting surface 24 associated with the press-fit fixation of the individual studs 12, 12. In view of these situations, Japanese Patent Unexamined Publication No. JP-A-2001-233001 describes a technique of improving the plane accuracy of the mounting surface 24 by machining to a part of the axially outboard surface of the mounting flange 8 which constitutes the mounting surface 24 (portions of the outboard surface shown as shaded with inclined lines in FIG. 29 which are offset radially inwards and outwards from a ring-like portion where the studs 12, 12 are arranged).
In addition, the perpendicularity of the mounting surface 24 relative to the rotational center axis of the hub 2, 2a to 2k is deteriorated by virtue of the deterioration of the perpendicularity of the geometric center axis of the cylindrical surface portion 9 formed on the outer circumferential surface of the hub main body 6, 6a to 6k {and the primary inner ring raceway 13a, 13c (and the inner surface 21 of the large collar portion 15)} (the parallelism of the individual portions) relative to the mounting surface 24. In view of these situations, the aforesaid Japanese unexamined patent publication, JP-A-2001-233001, further describes a technique of improving the plane accuracy of the mounting surface 24 in the way described above and thereafter improving the perpendicularity of the geometric center axis of the cylindrical surface portion 9 {and the primary inner ring raceway 13a, 13c (and the inner surface 21 of the large collar portion 15)} (the parallelism of the individual portions) relative to the mounting surface 24 by performing finishing work on the cylindrical surface portion 9 {and the primary inner ring raceway 13a, 13c (and the inner surface 21 of the large collar portion 15)} utilizing the mounting surface 24 as a reference surface.
In addition, the perpendicularity of the mounting surface 24 relative to the rotational center axis of the hub 2, 2a to 2k is deteriorated by virtue of the deterioration of rotational accuracy of a double row bearing which makes up the wheel supporting bearing unit. In order to improve the rotational accuracy of the double row bearing, it is important to, with respect to the primary and secondary inner rings 7a (7c), 7b (7d), improve the perpendicularity of the geometric center axis of the cylindrical inner circumferential surfaces of the inner races and the inner ring raceways formed on the outer circumferential surfaces of the inner races (and the inner surfaces 21 of the large collar portions 15) (the parallelism of these portions) relative to the large diameter side end faces of the inner races. In addition, in the case of the construction in which the primary inner ring raceway 13a, 13c is formed direct on the outer circumferential surface of the hub main body 6c to 6e, 6i to 6k, it is also important to improve the perpendicularity of the geometric center axis of the primary inner ring raceway 13a, 13c (and the inner surface 21 of the large collar portion 15) and the cylindrical surface portion 9 (the parallelism of these portions) relative to the mounting surface 24. In addition, in these cases, too, as with the technique described in JP-A-2001-233001, it is considered that the perpendicularity (or the parallelism) can be improved by finishing the large diameter side end faces of the primary and secondary inner rings 7a (7c), 7b (7d) and the mounting surface 24 with good plane accuracy and thereafter performing finishing work on the primary and secondary inner ring raceways 13a (13c), 13b (13d) (and the inner surfaces 21 of the large collar portions 15) and the cylindrical surface portion 9 utilizing the large diameter side end faces or the mounting surface 24 so finished as a reference surface.
As with the technique described in the aforesaid Japanese unexamined patent publication, JP-A-2001-233001, however, even in the event that the finishing work is performed on the individual portions utilizing as the reference surface the mounting surface 24 which is finished with good plane accuracy, in case a supporting surface of a support member which makes up a machining apparatus is not square to the rotational center axis of a spindle on which the support member is mounted, it becomes difficult to improve the perpendicularity (or the parallelism). Normally, the shape and dimensions of the support member are determined in design such that the supporting surface becomes square to the rotational center axis of the spindle in such a state that the support member is mounted on the spindle. In fact, however, since there exist a production error of the support member and a mounting error of the support member on to the spindle, there may occur a risk where the perpendicularity of the supporting surface relative to the spindle gets worse. When the supporting surface gets worse like this, it becomes difficult to improve the perpendicularity (parallelism).